1. Field of the Invention
The present invention relates to moving image display and recording technology applied to electronic cameras such as digital cameras, and more specifically to a technology which removes discontinuity in a moving image in the case where a still image is captured or aperture setting is changed while displaying or recording the moving image.
2. Description of the Related Art
Japanese Patent Application Publication No. 7-203288 discloses an image pickup apparatus, which has a high-resolution image-capturing mode and a standard-resolution image-capturing mode, and controls the switching of opening diameters of the apertures in accordance with a selected image-capturing mode.
However, if this image pickup apparatus employs an aperture mechanism (turret-type) in which multiple apertures having different opening diameters are formed on a movable aperture plate, the image-capturing optical path is temporarily blocked when the apertures are switched. An image immediately after the image-capturing modes are switched is thereby blocked, thus causing a defect of discontinuity in the moving image.
FIGS. 11 and 12 will be referred to for explanation. As shown in FIG. 11, a light transmitted through a lens 100 of a camera is subjected to light amount adjustment by an aperture 102, and then enters an image pickup device 104. The turret-type aperture mechanism has a structure that, as shown in FIG. 12, multiple apertures 112 having different opening diameters are formed on an aperture plate 110, and the aperture plate 110 rotationally moves about an axis 114 to selectively arrange one of the apertures 112 on the optical axis. During rotation of the aperture plate 110 for switching from a small aperture to a large aperture (or vice versa), the light is blocked by the aperture plate 110 and a period of non-capturing of moving image data is generated.
FIG. 13 is a timing chart showing this phenomenon. The image pickup device is driven in synchronization with a vertical drive signal (VD) corresponding to a video rate that defines reproduction timing. It is assumed that the aperture is initially set to “small aperture”, and movie exposure is performed during 1V period, then movie display or movie recording during the next 1V period is performed with data captured by the movie exposure.
If the apertures are switched from “small aperture” to “large aperture” with a drive timing shown as Ta in FIG. 13, the light is blocked by the aperture plate 110 during the driving period (Ta), and therefore, the data is missing from the image pickup device 104. Accordingly, during the next 1V period, the display is held in “non-display” condition (blackout). With respect to the recording process, there is a case where the black display is recorded during the period (recording method A) and another case where the data during the period is not recorded and the prior and subsequent data items are connected (recording method B). In both cases, the moving image discontinues, thus resulting in visually undesirable, unnatural reproduction of images.
After the 1V period shown as Ta in FIG. 13, the switching operation of the apertures is finished at the beginning of the next 1V period, and therefore, image data is normally captured from the image pickup device 104. In other words, with the image data captured by exposure after finishing the aperture changing operation, the movie display or movie recording is performed at the next vertical drive timing. Since the opening diameter of the aperture becomes larger, the image pickup light amount is increased. Accordingly, discontinuity of luminance in the moving image occurs before and after the aperture switching.
In the image pickup apparatus disclosed in Japanese Patent Application Publication No. 7-203288, the apertures are switched in response to switching of the image-capturing modes. However, a similar problem as described above occurs not only in the case where the image-capturing modes are switched, but also in the case where the apertures are switched in the same image-capturing mode.
There is a possibility that discontinuity in the moving image occurs not only when switching the apertures as described above, but also occurs when a still image is captured while capturing (recording) the moving image. Japanese Patent Application Publication No. 10-108121 discloses an electronic camera capable of recording both moving image and still image, in which if an instruction for recording a still image is given during recording of a moving image, image information from an image pickup device is temporarily stored in a buffer device in synchronization with the recording instruction, and after the recording process by a moving image recording device is finished, the image information (still image) stored in the buffer device is recorded on a recording medium. In this camera, a high priority is given to the moving image recording process and still image data is retained in the buffer, and therefore, the problem of discontinuity in the moving image does not occur. However, in a digital camera equipped with general multipixel CCD, the drive of the still image is performed while the drive of the moving image is suspended, and therefore, the blackout condition is generated during the period of capturing the still image. Especially, in the image pickup device using a mechanical shutter, the blackout condition becomes serious if the capturing of the still image takes a long time. The number of pixels in an image pickup device mounted to the digital camera has recently been increased and a device is developed which performs the capturing of still image with an enormous number of pixels up to several millions. Accordingly, since processes for still image capturing require some time, such problem has come to the surface.
FIG. 14 is referred to for explanation. The image pickup device is driven in synchronization with the vertical drive signal (VD). During the movie display, image data is read from the image pickup device within 1V period and the display or recording of the image data is carried out in the next 1V period. If an instruction for recording a still image is input while the movie display is performed, the drive for capturing the still image is carried out for several V periods. (In FIG. 14, capturing of the still image is carried out for 3V period, but in some cases the period will be longer.) Since it is impossible to acquire image data necessary for moving image display during the period of capturing the still image, the moving image display indicates “non-display (blackout)”. When capturing of the still image is finished and movie capturing is resumed, the movie display is also resumed in synchronization with the next vertical drive signal.
The same thing can be the for movie recording. During the period of non-reading of moving image data, there is a case where the black display is recorded during the period (recording method A) and another case where the moving image data during the period is not recorded and the prior and subsequent data items are connected after resuming data acquisition (recording method B). Both cases result in visually undesirable, unnatural reproduction of images.